ELECTROSTATIC-TYPE ELECTROMECHANICAL TRANSDUCER
In order to produce a larger output and smaller friction acting on a movable substrate of an electrostatic-type electromechanical transducer using electrostatic interaction between charged portions and opposing electrodes to transduce between electric power and motive power, the electrostatic-type electromechanical transducer includes: a fixed substrate; a movable substrate being movable while maintaining a predetermined distance between the fixed substrate and the movable substrate; charged portions disposed on a first surface of the movable substrate at intervals in a direction of movement of the movable substrate, the first surface facing the fixed substrate; opposing electrodes disposed on the fixed substrate in the direction of movement, the opposing electrodes facing the movable substrate; and a ground electrode facing a second surface of the movable substrate, the second surface being opposite to the first surface.
The present invention relates to an electrostatic-type electromechanical transducer in which an electret material is used.
BACKGROUNDElectrostatic-type electromechanical transducers, such as electrostatic motors and electric generators, which use charged films having the characteristics of semi-permanently carrying an electric charge are known (for example, see Patent Literature 1). Such electrostatic-type electromechanical transducers include charged films made of an electret material, and opposing electrodes facing the charged films. The electrostatic motors generate driving force by using electrostatic attraction between the charged films and the opposing electrodes, whereas the electric generators generate electric power by using electrostatic induction caused by fluctuations of the overlapping area therebetween. Such electrostatic-type electromechanical transducers are relatively compact, and are thus considered for adoption into portable electric equipment, such as a wristwatch, which a human wears and carries.
Patent Literature 1: Japanese Unexamined Patent Publication No. 2005-341675 (page 1. FIG. 2)
SUMMARYIt is known that the driving force f of an electrostatic motor in which an electret material is used is proportional to the product of the electric potential Vt of the charged films (charged portions) and the voltage Vb applied to the opposing electrodes. Therefore, the increase in the electric potential Vt of the charged films or the voltage Vb applied to the opposing electrodes leads to an increase in the driving force f. However, the increase in the voltage Vb applied to the opposing electrodes requires a boost of the voltage, and involves energy loss. Further, the increase in the electric potential Vt of the charged films requires an increase in the amount of electric charge stored in the charged films; however, there is a limit thereto.
Further, since attraction perpendicular to the surface of the movable substrate acts between the charged films and the opposing electrodes, as this attraction increases, the friction between the shaft supporting the movable substrate and its bearings becomes larger and increasingly prevents movement of the movable substrate. In this respect, the same applies to the electric generator in which an electret material is used.
The present invention is for addressing such a technical problem, and an object thereof is to provide an electrostatic-type electromechanical transducer which can produce a larger output, without large energy loss, and smaller friction acting on a movable substrate.
An electrostatic-type electromechanical transducer using electrostatic interaction between charged portions and opposing electrodes to transduce between electric power and motive power is provided. The electrostatic-type electromechanical transducer includes: a fixed substrate; a movable substrate being movable while maintaining a predetermined distance between the fixed substrate and the movable substrate; charged portions disposed on a first surface of the movable substrate at intervals in a direction of movement of the movable substrate, the first surface facing the fixed substrate; opposing electrodes disposed on the fixed substrate in the direction of movement, the opposing electrodes facing the movable substrate; and a ground electrode facing a second surface of the movable substrate, the second surface being opposite to the first surface.
Preferably, in the electrostatic-type electromechanical transducer, the ground electrode completely covers a region on the second surface of the movable substrate, the region corresponding to the places where the charged portions are disposed.
Preferably, in the electrostatic-type electromechanical transducer, the distance between the movable substrate and the fixed substrate is not less than 30 μm and not more than 150 μm.
In the electrostatic-type electromechanical transducer, the movable substrate and the fixed substrate may be disposed between a top plate and a main plate, and the ground electrode may be formed on the top plate or the main plate, and face the movable substrate. Alternatively, the movable substrate and the fixed substrate may be disposed between a top plate and a main plate, and the top plate or the main plate may serve as the ground electrode.
Preferably, in the electrostatic-type electromechanical transducer, the movable substrate is rotatable around a rotating shaft passing through the center of the movable substrate, and the charged portions and the opposing electrodes are radially disposed around the rotating shaft.
Preferably, the electrostatic-type electromechanical transducer further includes: a driving unit applying an alternating voltage to the opposing electrodes to generate electrostatic force between the charged portions and the opposing electrodes, thereby rotating the movable substrate; and a gear train coupled to the rotating shaft on the side opposite to the movable substrate with respect to the ground electrode, the gear train rotating together with the movable substrate to transmit rotational motion of the movable substrate to the outside of the electrostatic-type electromechanical transducer.
Alternatively, the electrostatic-type electromechanical transducer preferably further includes: a gear train coupled to the rotating shaft on the side opposite to the movable substrate with respect to the ground electrode, the gear train being driven by an external power source to rotate the rotating shaft and the movable substrate; and a charging unit storing electric power generated by electrostatic induction between the charged portions and the opposing electrodes in response to rotation of the movable substrate.
The electrostatic-type electromechanical transducer can produce a larger output, without large energy loss, and smaller friction acting on a movable substrate.
Hereinafter, with reference to the accompanying drawings, electrostatic-type electromechanical transducers will be explained in detail. However, it should be noted that the present invention is not limited to the drawings or the embodiments described below.
As shown in
The material of the movable substrate 101 may be a dielectric, such as alumina and zirconia, a metal, such as copper and aluminum, or a semiconductor, such as silicon (Si). The movable substrate 101 is electrically insulated from the other components by using an insulator for the shaft 107 or the bearings 109 or fixing the bearings 109 to the top plate 113 and the main plate 111 with an insulating bonding layer interposed therebetween.
As shown in
The charged films 125 are an example of the charged portions, and are formed on the lower surfaces of the connecting portions 123 of the movable substrate 101 (on the first surface facing the fixed substrate 103), as shown in
The fixed substrate 103 is a driving-electrode substrate on which the opposing electrodes (driving electrodes) 129 for driving the movable substrate 101 are disposed, and is made of a well-known substrate material, such as a glass epoxy substrate. The fixed substrate 103 has a disk shape, for example, as shown in
The opposing electrodes 129 are divided into two groups of opposing electrodes 129A and opposing electrodes 129B, and each of these groups is composed of substantially trapezoidal electrodes, as shown in
The driving circuit 127 is an example of the driving unit, and includes a clock 131 and two comparators 133. As shown in
The driving circuit 127 applies an alternating voltage whose polarity is alternately reversed to the opposing electrodes 129 in this manner, to continuously generate electrostatic force between the charged films 125 and the opposing electrodes 129, thereby rotating the movable substrate 101. The force applied to the charged films 125 is divided into a component acting in the horizontal direction of
The ground electrode 105 is an electrically grounded electrode, and is disposed between the movable substrate 101 and the top plate 113, on the side opposite to the fixed substrate 103 with respect to the movable substrate 101. In other words, the ground electrode 105 faces the second surface of the movable substrate 101, the second surface being opposite to the first surface facing the fixed substrate 103. In order to ground the ground electrode 105 outside the electrostatic motor 100, the ground electrode 105 is preferably disposed so as to penetrate the supports 115, for example, as shown in
However, the ground electrode 105 need not necessarily cover the entire surface of the movable substrate 101. For example, the ground electrode 105 need not necessarily cover the center portion 101A and the outer portion 101B of the movable substrate 101, and neither need it cover some of the connecting portions 123 if it covers most of the connecting portions 123.
Alternatively, if the positions of the fixed substrate 103 and the movable substrate 101 are reversed and the fixed substrate 103 is disposed on the side closer to the top plate, the main plate 111 may be grounded for use as the ground electrode 105. Further, without using the top plate 113 or the main plate 111 as the ground electrode 105, the ground electrode 105 may be separately provided on the top plate 113 or the main plate 111 so as to face the movable substrate 101. In this case, the ground electrode 105 may be disposed, for example, on the entire surface of the top plate 113 or the main plate 111, or only some of that surface.
As shown in
If only the driving force is taken into consideration, it is preferred that the distance d1 between the charged films 125 and the opposing electrodes 129 be as small as about several tens of micrometers. However, even if the distance d1 is about 300 μm, the driving force of the electrostatic motor 100 is larger than that of the electrostatic motor 200; and thus, the distance d1 may be in the range from several tens of micrometers to about 300 μm. A larger distance d1 makes the assembly of the electrostatic motor 100 easier.
In the electrostatic motor 200, the normal force is negative as shown in
The graphs in
As described above, the electrostatic motor 100 includes a ground electrode 105 disposed at a place facing a surface of the movable substrate 101, which surface is not provided with the charged films 125. In the electrostatic motor 100, this makes the driving force larger, improves tolerance to variations of a load and to external perturbations, and reduces the friction between the shaft 107 and the bearings 109 to make the loss of driving force smaller.
In the electric generator 150 also, as is the case with the electrostatic motor 100 shown in
The rotation of the movable substrate 101 increases and decreases the overlapping area between the charged films 125 of the movable substrate 101 and the opposing electrodes 129A and 129B. Along with this, the electric field generated by the charged films 125 increases and decreases the electric charge attracted to the opposing electrodes 129A and 129B. The electric generator 150 uses electrostatic induction in this manner to generate an alternating current between the opposing electrodes 129A and the opposing electrodes 129B, thereby generating electric power.
The charging circuit 151 includes a rectifier circuit 153 and a storage battery 155. The charging circuit 151 is an example of the charging unit, and stores electric power generated by electrostatic induction between the charged films 125 and the opposing electrodes 129A and 129B in response to the rotation of the movable substrate 101. The opposing electrodes 129A and 129B of the electric generator 150 are connected to the rectifier circuit 153 through electric wiring, and the rectifier circuit 153 is connected to the storage battery 155. The rectifier circuit 153 is a bridge circuit including four diodes, and rectifies the current generated between the opposing electrodes 129A and the opposing electrodes 129B. The storage battery 155 is a chargeable and dischargeable battery, such as a lithium-ion battery, stores the electric power generated by the electric generator 150, and supplies the electric power to a circuit (not shown) to be driven.
The electric generator 150 also includes a ground electrode 105 disposed at a place facing a surface of the movable substrate 101, which surface is not provided with the charged films 125. This increases the apparent surface potential V of the charged films 125, and correspondingly increases the amount of generated electric power. Further, the electric generator 150 also has the effect of reducing the friction between the shaft 107 and the bearings 109, similarly to the electrostatic motor 100.
The rotation-type electrostatic motor and electric generator have been described above. However, since the important thing is to provide a ground electrode on the side opposite to the fixed substrate with respect to the movable substrate, it is clear that electrostatic motors and electric generators in which the movable substrate reciprocates also have the same advantageous effect.
Claims
1. An electrostatic-type electromechanical transducer using electrostatic interaction between charged portions and opposing electrodes to transduce between electric power and motive power, the electrostatic-type electromechanical transducer comprising:
- a fixed substrate;
- a movable substrate being movable while maintaining a predetermined distance between the fixed substrate and the movable substrate;
- charged portions disposed on a first surface of the movable substrate at intervals in a direction of movement of the movable substrate, the first surface facing the fixed substrate;
- opposing electrodes disposed on the fixed substrate in the direction of movement, the opposing electrodes facing the movable substrate; and
- a ground electrode facing a second surface of the movable substrate, the second surface being opposite to the first surface.
2. The electrostatic-type electromechanical transducer according to claim 1, wherein the ground electrode completely covers a region on the second surface of the movable substrate, the region corresponding to the places where the charged portions are disposed.
3. The electrostatic-type electromechanical transducer according to claim 1, wherein the distance between the movable substrate and the fixed substrate is not less than 30 μm and not more than 150 μm.
4. The electrostatic-type electromechanical transducer according to claim 1, wherein
- the movable substrate and the fixed substrate are disposed between a top plate and a main plate, and
- the ground electrode is formed on the top plate or the main plate, and faces the movable substrate.
5. The electrostatic-type electromechanical transducer according to claim 1, wherein
- the movable substrate and the fixed substrate are disposed between a top plate and a main plate, and
- the top plate or the main plate serves as the ground electrode.
6. The electrostatic-type electromechanical transducer according to claim 1, wherein
- the movable substrate is rotatable around a rotating shaft passing through the center of the movable substrate, and
- the charged portions and the opposing electrodes are radially disposed around the rotating shaft.
7. The electrostatic-type electromechanical transducer according to claim 6, further comprising:
- a driving unit applying an alternating voltage to the opposing electrodes to generate electrostatic force between the charged portions and the opposing electrodes, thereby rotating the movable substrate; and
- a gear train coupled to the rotating shaft on the side opposite to the movable substrate with respect to the ground electrode, the gear train rotating together with the movable substrate to transmit rotational motion of the movable substrate to the outside of the electrostatic-type electromechanical transducer.
8. The electrostatic-type electromechanical transducer according to claim 6, further comprising:
- a gear train coupled to the rotating shaft on the side opposite to the movable substrate with respect to the ground electrode, the gear train being driven by an external power source to rotate the rotating shaft and the movable substrate; and
- a charging unit storing electric power generated by electrostatic induction between the charged portions and the opposing electrodes in response to rotation of the movable substrate.
Type: Application
Filed: Mar 16, 2017
Publication Date: Mar 14, 2019
Patent Grant number: 10622917
Inventor: Izumi YAMAMOTO (Saitama)
Application Number: 16/084,537